The end of our Chapter 42 was a testificatory Amen. In Nephite tradition, that required the end of a chapter. However, it wasn’t the end of the story, so the first two verses of our Chapter 43 end the story of Alma’s sons. In Alma 42:31, Alma commissioned Corianton to preach the gospel. Verse 1 in this chapter tells us that Corianton and his brothers, as well as his father, did go forth to preach.
Mormon wanted to include the counsel to the sons, but he didn’t want to add anything about that particular preaching journey. He tells his audience “now we shall say no more concerning their preaching.” The only thing he says is that they preached through the spirit of prophecy and revelation. Unlike the discussion of Alma’s missionary journey within the land of Zarahemla and the stories of the sons of Mosiah, Mormon gives his readers no details whatsoever of these journeys.